Around one in five trains are expected to operate today as railway workers hold the first of three strike days this week.
Thousands of staff employed by Network Rail and 13 train operators are on picket lines today. They are due to walk out again on Thursday, June 23 and Saturday June 25 because of the dispute.
Members of the Rail, Maritime and Transport (RMT) union are taking part in the strike. The dispute is about jobs, pay and conditions. But what does that mean?